Magnetoresistive Random Access Memory (MRAM) is an emerging technology that may be competitive with prior integrated circuit memory technologies, such as floating gate technology. The MRAM technology may integrate silicon-based electronic components with magnetic tunnel junction (MTJ) technology. A significant element in MRAM is the MTJ where information may be stored as memory. A MTJ stack has at least two magnetic layers separated by a non-magnetic barrier layer, where a first magnetic layer (the fixed layer) has a set magnetic property and a second magnetic layer (the free layer) has a programmable magnetic property. The MTJ stack can store information based upon the programmable state of the second (free) magnetic layer. “Programming,” as used herein, refers to changing the state of a memory cell such that the stored information of the memory cell is changed. More particularly, if the fixed layer and the free layer have parallel magnetic poles, the resistance through the MTJ stack is measurably less than if the fixed layer and the free layer have anti-parallel poles, so parallel magnetic poles may be read as a “0” and anti-parallel poles may be read as a “1.” Therefore, the MTJ stack and the memory cell are programmed by changing the alignment of the free layer relative to the fixed layer.
The free layer is programmed with electric current, but the properties of the required programming electric current depend on temperature. A larger electric current is required at a lower temperature. For example, to change the polarity of the free layer at a temperature of about 125 degrees Celsius (° C.), a word line voltage of about 1.7 volts combined with a source line voltage of about 0.7 volts may be required. However, to change the polarity at a temperature of about −40° C., a word line voltage about 2.1 volts and a source line voltage of about 0.8 volts may be required to deliver a larger current. Excessive voltage can damage the MTJ stack, and the voltage that can damage the MTJ stack depends on temperature. Therefore, consistent use of higher voltages is not acceptable. To address this issue, the temperature of the memory cell may be determined, and the required voltage for a write operation (a programming charge of electrical energy) is determined based on the temperature. Analog circuits are then activated to generate the write operation at the required voltage for the temperature. However, the analog circuits are complex, and have a relatively large footprint in an integrated circuit.
Accordingly, it is desirable to provide integrated circuits with memory cells that can be programmed with a substantially constant voltage write operation that is independent of temperature, and methods of producing the same. In addition, it is desirable to provide integrated circuits with magnetoresistive memory cells that can be programmed with digital circuits, as opposed to analog circuits, and methods of producing the same. Furthermore, other desirable features and characteristics of the present embodiment will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.